The present invention relates to the field of water purification. More specifically, it relates to the field of treatment of water in view of eliminating therefrom any bacteria of the genus Legionella, in particular of the species Legionella pneumophila, using an apparatus and a method wherein an ozone containing gas is utilised.
The legionnaire""s disease is caused by the pathogen Legionella pneumophila, which is a common microorganism in nature. The legionnaire""s disease, as well as other diseases caused by Legionella bacteria, are severe conditions of epidemiological character which have even been known to cause death. More specifically, the bacteria will colonize water supply systems, water heaters, showers, jacuzzi whirl pools etc. Severe problems have e.g. been observed in hospitals, in which cases the only solution has been to change the already colonized pipings to all new equipment. Other fields where contamination by Legionella has been seen to cause problems are e.g. in the aerosol and rinse water of dentists and dental surgeons.
Temperatures of between 30-40xc2x0 C. have been shown optimal for the growth of Legionella bacteria. In such an environment, a kind of biological film, or biofilm, comprising various bacteria and microorganisms, will appear. Some materials in pipes and packings as well as where air pockets are formed, will enhance growth of the Legionella bacteria. In our modern society, in order to reduce costs, energy consumption often is lowered by decreasing the temperature of the hot tap water, whereby the growth of Legionella bacteria is in fact encouraged, in turn resulting in an increased number of individuals afflicted with the diseases caused by Legionella. Accordingly, there is an increased need of methods which effectively control Legionella colonization at reasonable costs.
Prior art methods of eliminating Legionella are by hyperchlorination, thermal treatment. UV radiation, by adding metal ions such as copper and silver ions. Of these, the simplest method has been the thermal treatment, i.e. heating the water to a temperature sufficient to kill the Legionella bacteria present therein, a method which however suffers from the drawback of increased energy costs and risks of skin bums by hot tap water. On the other hand, hyperchlorination has the main disadvantage of corroding the water piping system and of possible production of carcinogenic by-products. UV treatment may give rise to the formation of calcareous deposits on the UV source, reducing the efficiency of the treatment, and to a possible damage of the lamps by contact with water. In the chemical water treatment with metal ions there is an inherent risk of pollution of the water by the chemicals added. Another proposed method is to kill the bacteria by use of 70% ethanol. The use of ethanol, however, gives rise to a fire risk. Moreover, the remedy obtained using these methods is only temporary and with time the contamination problem is susceptible of reappearing.
Ozone has been suggested in the prior art for the control of various microorganisms. In nature, ozone is formed in the stratosphere and forms a layer protecting life on earth from deleterious UV radiation. Ozone as such is a strong oxidant and a toxic gas capable of quickly and efficiently killing bacteria and virus. Accordingly, correctly used, ozone may be an advantageous disinfectant, even though caution must be exercised to avoid harm on the environment and human beings.
It is known to use ozone in high concentrations for disinfecting water from contamination by e.g. Legionella species. Indeed, U.S. Pat. No. 5,882,588 describes a process for continuously disinfecting hot water using ozone. More specifically, said patent relates to the use of heat transfer means to achieve hot water, of a temperature around 50xc2x0 C. which under a reduced pressure is brought to a treatment tank. Meanwhile, an ozone containing gas, having a concentration of ozone of preferably 2-10%, is fed to the treatment tank from an ozonizer, wherein ozone has been produced from oxygen. The pH is controlled in said tank by addition of HCl. In this patent it also is stated: xe2x80x9cIt can be learned from scientific literature that a dose of 1-2 mg/l of ozone is expedient for the treatment of tap waterxe2x80x9d.
In the preferred embodiment of the above cited U.S. Pat. No. 5,882,588 the ozone containing gas is introduced into the hot water in the reactor by passing it through a ceramic frit or analogous distribution means, so that the ozone containing gas passes through the water in the form of bubbles. Another patent, U.S. Pat. No. 6,001,247 relates to an improved ozone dissolution system, wherein a sidestream venturi injection system is combined with a specially, designed downflow tube. The advantageous effect provided by this patent is a decreased risk of the gas bubble channelling which may occur when higher ozone concentrations, such as 8-12% by weight, are combined with lower gas flows. The system according to this patent is however a complicated apparatus comprising several diffusion chambers, reaction tanks etc, which requires a complex setting of tubing.
Application of ozone as a disinfectant also has been proposed in WO 981647, A2 (Long, Ron). This patent application relates to a point-of use filtration and ozonation drinking water treatment system and process. The amount of ozone to be injected into the water in order to disinfect it is not indicated. However a retained ozone residual of between 0.1 and 0.4 parts per million in the disinfected water is mentioned, and it is stated that the ozone-containing water so produced may be of use i.a. for rinsing surfaces, articles and food to reduce microbiological contamination thereof.
Another patent application, EP 0315508 A1 (Kishioka, Takashi) relates to an ozonic bubble water generator which generates ozonic bubble water by mixing ozone into water. The ozonic bubble water is proposed for use e.g. as a disinfecting hand wash. Thus, as in WO 9816473 A2. cited above, an outflow of ozonized water is proposed for use as a disinfectant.
DK 166452 B1 (I. Krueger A/S) relates to a method of ground water treatment wherein ozone is used to sterilise water which has been used to rinse filters for the ground water. It is stated that at an ozone concentration of 0.01 mg/l, as much as 99.9% of the microorganisms present in the rinse water are killed within 1 minute. The ozone treatment of the water preferably is performed in a closed reaction tank and the treated water then is returned to the inlet for the non-treated ground water where any residual ozone in the treated water is used in an oxidation reaction of the incoming ground water.
From the above it appears that ozone has been used in various applications, including for treating water in order to eliminate Legionella therefrom. However, until now it has not been possible to eliminate, in a reliable, economical and simple way. Legionella from a system of a flowing water and possibly water droplet aerosol, by use of a very low ozone level and a very short treatment time, permitting to obtain a water outflow and water droplet aerosol which are also essentially free from ozone. This is the object of the present invention.
in contrast to the teachings of the prior art documents, according to the present invention elimination of essentially all of Legionella bacteria present in a flow of water is obtained
at a much lower level of injected ozone, and
by a much shorter treatment time,
and this makes possible the treatment of the water flow by an apparatus located in close vicinity to the outlet for the flow of water without any risk of outflowing water contaminated with harmful levels of ozone.
The location of the point of treatment in close vicinity to the outlet results in the further advantage of reducing the risk of re-contamination of the water with Legionella downstream of the point of treatment, which re-contamination could occur in case the point of treatment be located farther back upstream in the water supply system.
Consequently, according to the invention, by use of a level of injected ozone as low as 0.01-0.5 mg/liter of water, an essentially total elimination, i.e. killing, of all Legionella bacteria present in a flow of water is obtainable within an extremely short time period of treatment, such as less than one second.
Thus, in a first aspect, the present invention relates to an apparatus for purifying a flow of water, by eliminating any Legionella bacteria present therein which apparatus comprises
(a) means for providing ozone;
(b) means for injecting the ozone into the flow of water;
(c) a mixing chamber for mixing the ozone with the flow of water;
(d) an outlet for the flow of water, and
(e) electronic control means for the operation thereof;
wherein the mixing chamber is of an inner geometry such as to create turbulence in the flow of water therein.
Thus, according to an aspect of the invention an apparatus for eliminating Legionella present in a flow of water is provided.
Indeed, the mixing chamber is of an inner geometry geometry such as to provide an essentially total elimination of any Legionella bacteria present in the flow of water entering the mixing chamber.
In a further aspect a method of obtaining a purified flow of is provided, which method comprises the steps of
(a) providing ozone;
(b) injecting the ozone into a flow of water susceptible of containing Legionella bacteria.
(c) mixing the ozone with the flow of water within a mixing chamber; and
(d) directing the flow of water to an outlet
wherein the mixing of the ozone with the water in step (d) is accomplished by creating turbulence in the flow of the water within the mixing chamber.
By the method of the invention a flow of water free from Legionella bacteria is obtained. It thus is an advantageous aspect of the present method that an essentially total elimination of any Legionella bacteria present in the flow of water entering the mixing chamber is achieved to provide a flow of water which is essentially free from any Legionella bacteria on exiting from the mixing chamber.
Thus, according to a very advantageous aspect the invention present provides a simple, reliable and economical method of eliminating Legionella from a flow of water, such as tepid water for taps or showers, without any risk of a possible presence of any harmful residual treatment chemical in the water delivered to the user, as well as an apparatus therefor.
It is a very advantageous aspect of the invention that elimination of Legionella is achievable directly on-line in the flow of water essentially without any delay after actuating the valve regulating the outflow of water.
Aspects of the invention are further defined by the appended claims.